High-strength and high-toughness hydrogen-resistant lining material for hydrogen storage container and preparation method of high-strength and high-toughness hydrogen-resistant lining material

Abstract

The invention relates to the technical field of hydrogen-resistant lining materials, and provides a hydrogen-resistant lining material for a high-strength and high-toughness hydrogen storage container and a preparation method of the hydrogen-resistant lining material, the hydrogen-resistant lining material comprises the following components: modified carbon nanofiber, anhydride modified ethylene copolymer and polyamide; the modified carbon nanofiber is of a core-shell structure, and the core-shell structure takes carbon nanofiber as a core and takes graphene oxide as a shell; the carbon nanofibers are grafted with amino groups; performing electrostatic winding on amino and graphene oxide; in the components, the carbon nanofibers are grafted with amino groups to realize cationization modification, so that the Zeta potential of the carbon nanofibers is changed from negative to positive, so that a graphene oxide sheet layer with negative electricity is tightly wound on the surface of the carbon nanofibers at a specific angle, and a core-shell structure in which the carbon nanofibers are tightly wrapped by the graphene oxide sheet layer is further formed; the graphene oxide shell layer effectively covers defects and microcracks on the surface of the carbon nanofiber, eliminates a short-circuit channel for hydrogen permeation, and improves the hydrogen resistance effect.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and specifically relates to a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container and a preparation method thereof. Background Art

[0002] As a clean and renewable energy source, the widespread application of hydrogen energy depends on safe and efficient storage and transportation containers. For example, Type IV hydrogen storage bottles are important carriers for hydrogen energy storage and transportation due to their lightweight, high pressure and high hydrogen storage density. However, the key lining material of Type IV hydrogen storage bottles is mainly polyamide 6 (PA6), but its brittle characteristics pose a safety hazard that may cause material failure, thereby restricting the safety performance of hydrogen storage bottles.

[0003] In the existing technology, elastomer toughening (such as ethylene-α-olefin copolymer elastomer, EPDM rubber, etc.) is usually used to absorb energy by inducing shear yield of the matrix, but this often comes at the expense of the material's rigidity and thermal deformation temperature. In addition, the existing technology also introduces rigid fillers (such as glass fiber, carbon fiber, etc.) to improve strength, but the fiber and matrix interface compatibility is poor, which easily causes stress concentration. More importantly, its interfacial bonding with PA6 is weak, and hydrogen molecules easily diffuse along the fiber / matrix interface, forming a permeation channel, which is then easily broken and produces microcracks during high-pressure hydrogen storage, further accelerating hydrogen penetration.

[0004] Therefore, based on the above description, there is an urgent need for a lining material for a hydrogen storage container that has good hydrogen barrier effect, high strength and high toughness, and a preparation method thereof. Summary of the Invention

[0005] Technical Problems Solved by the Invention The existing hydrogen barrier lining materials based on polyamide 6 have the technical problem of being difficult to achieve both high strength, high toughness and good hydrogen barrier effect.

[0006] Technical solution adopted by the present invention In view of the above-mentioned deficiencies, the object of the present invention is to provide a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container and a preparation method thereof.

[0007] The specific contents are as follows: First, the present invention provides a high-strength and high-toughness hydrogen storage container hydrogen barrier lining material, the components of which, by weight, include 0.5 to 1.2 parts of modified carbon nanofiber, 10 to 15 parts of an anhydride-modified ethylene copolymer, and 84 to 89 parts of polyamide 6; The modified carbon nanofiber is a core-shell structure, wherein the core-shell structure has carbon nanofiber as a core and graphene oxide as a shell; the carbon nanofiber is grafted with amino groups; and the amino groups are electrostatically entangled with the graphene oxide.

[0008] Second, the present invention provides a method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container, comprising the following steps: The steps include: S1. Dispersing carbon nanofibers in deionized water, adding polyethyleneimine and stirring to react, washing by centrifugation until neutral, and freeze-drying to obtain amino-modified carbon nanofibers; S2. blending the amino-modified carbon nanofibers and the graphene oxide dispersion according to a certain proportion, centrifuging and freeze-drying to obtain modified carbon nanofibers; S3: banburying and blending the modified carbon nanofibers and the anhydride-modified ethylene copolymer to obtain a premix; S4 melt-blending the premix, polyamide 6 and composite nucleating agent, and extruding and granulating to obtain a molding masterbatch; S5: After annealing the molding masterbatch, plasma treatment is performed using a fluorocarbon precursor to obtain a finished material.

[0009] Technical mechanism and beneficial effects of the present invention The present invention uses a cationic modifier to graft amino groups onto the surface of carbon nanofibers (CNFs), achieving cationic modification and converting their zeta potential from negative to positive, so that negatively charged graphene oxide (GO) sheets can tightly wrap around their surface at a specific angle. Ultimately, through an electrostatic self-assembly reaction, a core-shell structure is formed in which the GO sheets tightly wrap around the CNFs. The GO shell effectively covers defects and microcracks on the CNF surface, eliminating short-circuit channels for hydrogen penetration and improving the hydrogen barrier effect. Furthermore, because GO is indirectly connected to the core CNF through an electrostatic self-assembly reaction with amino groups, a nanoscale tortuous maze structure is formed, the diffusion path and diffusion rate of hydrogen molecules are extended, further improving the hydrogen barrier effect. At the same time, the abundant oxygen-containing functional groups on the GO surface form a strong hydrogen bond network with the polymer matrix polyamide 6 (PA6), which not only enhances the interfacial bonding strength and reduces the free hydrogen concentration, but also further improves the hydrogen barrier effect.

[0010] The present invention adopts a premixing process, first mixing the modified CNF and the elastomer anhydride-modified ethylene copolymer in a premixed manner, and then precisely controlling the shear force field to allow the CNF to penetrate the anhydride-modified ethylene copolymer to form a preassembled three-dimensional continuous network. This unique cross-phase network structure can achieve effective stress transfer, causing the stress field around the anhydride-modified ethylene copolymer particles to produce a superposition effect. When the subsequent polymer matrix PA6 is added, it can induce a large-scale shear yield of PA6, thereby improving the toughness of the material and optimizing the stress distribution to avoid stress concentration. The rapid crack propagation caused by this process is further suppressed by the composite nucleating agent, which synergistically induces PA6 to form a mixed structure of α and γ crystals. Specifically, due to its small molecular size and high polarity, organic phosphates are enriched at the CNF / PA6 interface through electrostatic and hydrogen bonding, inducing the epitaxial growth of γ crystals. At the same time, hydroxyapatite nanoparticles are retained in the bulk phase due to volume restrictions, and promote the formation of α crystals by virtue of lattice matching. This gradient crystal structure is jointly regulated by the interface chemical matching and the bulk crystallization kinetics, forming a synergistic reinforcement mechanism of "interface γ crystal barrier-matrix α crystal toughening".

[0011] After annealing the composite material, the present invention performs plasma treatment again to further construct a nanoscale fluorocarbon barrier layer on the material surface. This layer has a dense cross-linked network structure, which can further effectively block the penetration of hydrogen molecules. More importantly, the surface treatment can be limited to the outermost layer of the composite material, thereby effectively avoiding the adverse effects of overall fluorination on the toughness of the material. DETAILED DESCRIPTION

[0012] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0013] Example 1 This embodiment provides a method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container: Raw materials preparation: Polyamide 6: brand TP4208, density 1.14g / cm 3 , the melt flow rate is 5.5g / min (225℃ / 2.16kg).

[0014] Carbon nanofibers: with a diameter of 150-200 nm, a length of about 10-20 μm, and a purity higher than 99.9%, were purchased from Beijing Dekedaojin Co., Ltd.

[0015] Elastomer: An anhydride-modified ethylene-based copolymer (AEC), brand N493, produced by DuPont in the United States.

[0016] The dosage of the components is: by mass, 0.5 parts of modified carbon nanofiber, 10 parts of anhydride-modified ethylene copolymer (AEC), 89 parts of polyamide 6, and 0.5 parts of a composite nucleating agent (wherein the weight ratio of nano-hydroxyapatite to organic phosphate is 1:1).

[0017] Preparation method and process parameters: Step S1: Preparation of amino-modified carbon nanofibers The carbon nanofibers were dispersed in deionized water and ultrasonically treated for 30 minutes; polyethyleneimine was added and stirred at 60° C. for 4 hours; the mixture was centrifuged and washed until neutral, and freeze-dried to obtain amino-modified carbon nanofibers.

[0018] Step S2: Preparation of modified carbon nanofibers 1 mL of a 1 mg / mL graphene oxide dispersion was mixed with 2.5 g of amino-modified carbon nanofibers (ratio 1 mL:2.5 g). Ultrasonic-assisted stirring was performed for 2 h, followed by centrifugation and freeze-drying to obtain core-shell structured modified carbon nanofibers.

[0019] Step S3: Preparation of premix 0.5 parts of modified carbon nanofibers and 10 parts of anhydride-modified ethylene copolymer were added to an internal mixer and mixed at 180° C. and 60 rpm for 15 minutes to obtain a premix.

[0020] Step S4: melt blending and extrusion granulation Add the premix, polyamide 6 and composite nucleating agent into the twin-screw extruder, and melt blending parameters are as follows: Extrusion speed: 100rpm; Barrel zone temperatures: Zone 1 175°C, Zone 2 190°C, Zone 3 205°C, Zone 4 220°C, Zone 5 235°C, Zone 6 230°C; Extrusion granulation parameters: Heating temperature of each zone of the injection molding machine: Zone 1 210℃, Zone 2 215℃, Zone 3 223℃, Zone 4 220℃, Zone 5 200℃; The injection time is 10s, the cooling time is 40s, and the ejection time is 2s to obtain the molding masterbatch.

[0021] Step S5: Annealing and plasma treatment The masterbatch was annealed at 150 °C for 2 h; Hexafluoropropylene was used as a fluorocarbon precursor, and the plasma treatment parameters were: power 100 W, time 5 min, and temperature 25° C. to obtain the finished material.

[0022] Example 2 The difference between this embodiment and embodiment 1 is that the amount of components used is: by weight, 0.85 parts of modified carbon nanofiber, 12 parts of anhydride-modified ethylene copolymer (AEC), 85 parts of polyamide 6, and 1.25 parts of composite nucleating agent (wherein the weight ratio of nano-hydroxyapatite to organic phosphate is 1:1.25). 2. Preparation method and process parameters Step S1: Preparation of amino-modified carbon nanofibers After the carbon nanofibers were dispersed, polyethyleneimine was added and stirred at 62.5°C for 5 h.

[0023] Step S2: Preparation of modified carbon nanofibers 1.1 mL of a graphene oxide dispersion with a concentration of 1 mg / mL was taken and blended with 2.25 g of amino-modified carbon nanofibers (amount ratio of 1.1 mL:2.25 g).

[0024] Step S3: Preparation of premix The modified carbon nanofibers and AEC were mixed at 182.5°C and 65 rpm for 22.5 min to obtain a premix.

[0025] Step S4: melt blending and extrusion granulation Extrusion speed: 105rpm; Barrel zone temperatures: Zone 1 177.5°C, Zone 2 192.5°C, Zone 3 207.5°C, Zone 4 222.5°C, Zone 5 237.5°C, Zone 6 232.5°C; Extrusion granulation temperature: zone 1 211℃, zone 2 216.5℃, zone 3 224℃, zone 4 221.5℃, zone 5 202.5℃.

[0026] Step S5: Annealing and plasma treatment Plasma treatment parameters: power 200 W, time 17.5 min, temperature 52.5 °C.

[0027] Example 3 The difference between this embodiment and Example 1 is that the component usage is: in parts by mass, 1.2 parts of modified carbon nanofiber, 15 parts of anhydride-modified ethylene copolymer (AEC), 82 parts of polyamide 6, and 1.5 parts of composite nucleating agent (wherein the weight ratio of nano-hydroxyapatite to organophosphate is 1:1.5).

[0028] 2. Preparation method and process parameters Step S1: Preparation of amino-modified carbon nanofibers After adding polyethyleneimine, the reaction was stirred at 65°C for 6 h.

[0029] Step S2: Preparation of modified carbon nanofibers 1.2 mL of graphene oxide dispersion with a concentration of 1 mg / mL was taken and blended with 2 g of amino-modified carbon nanofibers (amount ratio of 1.2 mL:2 g).

[0030] Step S3: Preparation of premix The modified carbon nanofibers and AEC were mixed at 185°C and 70 rpm for 30 min to obtain a premix.

[0031] Step S4: melt blending and extrusion granulation Extrusion speed: 110rpm; Barrel zone temperatures: Zone 1 180°C, Zone 2 195°C, Zone 3 210°C, Zone 4 225°C, Zone 5 240°C, Zone 6 235°C; Extrusion granulation temperature: zone 1 212℃, zone 2 218℃, zone 3 225℃, zone 4 223℃, zone 5 205℃.

[0032] Step S5: Annealing and plasma treatment Plasma treatment parameters: power 300 W, time 30 min, temperature 80 °C.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the carbon nanofibers are not modified.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that no composite nucleating agent is added.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that the anhydride-modified ethylene copolymer is not used, and the modified carbon nanofibers are melt-blended with polyamide 6 and a composite nucleating agent.

[0036] Comparative Example 4 The difference between this comparative example and Example 1 is that no plasma treatment is performed.

[0037] Test example Using Examples 1-3 and Comparative Examples 1-4 as samples, the mechanical and barrier properties of the samples were measured. Mechanical properties were tested according to the international measurement standard ASTM D 256-04, using an XC-22Z impact tester (Chengde Jinjian, China) to measure notched impact strength. Impact specimens were prepared by microinjection molding, with notches pre-milled to a uniform depth of 2 mm. The impact strength of the specimens was tested at two temperatures: 23°C and 0°C. To test the impact strength of the specimens at 0°C, the specimens were immersed in an ice-water mixture for 4 hours and then immediately removed and tested. Tensile properties were tested according to ISO 527 using a UTM4104X universal tensile tester (Sansi Zongheng, China). Testing was performed at room temperature (23°C) at a tensile speed of 50 mm / min.

[0038] The barrier properties include water vapor barrier test and oxygen barrier test. The water vapor barrier test refers to GB1037-88, and the oxygen barrier test refers to GB1038-2000. The test results are shown in Table 1.

[0039] Table 1 Sample performance test results

[0040] According to the above table data: The impact strength of Example 1 to Example 3 increases successively from 46KJ / m 2 to 67KJ / m 2 This is because, as the CNF content increases, amino groups are grafted onto the CNF surface through the cationic modifier, forming a core-shell structure with the negatively charged GO sheets. The GO shell covers the surface defects of the CNF, eliminating the short-circuit channel for hydrogen permeation. At the same time, the oxygen-containing functional groups on the GO surface form a strong hydrogen bond network with PA6, enhancing the interfacial bonding strength. In the premixing process, CNF and anhydride-modified ethylene copolymer are premixed to form a three-dimensional continuous network, which induces large-scale shear yield of PA6, improves toughness, avoids stress concentration, and thus significantly improves impact strength. At the same time, the tensile strength of Examples 1 to 3 gradually increased from 38 MPa to 45 MPa. This is due to the uniform dispersion of CNF in the PA6 matrix, and its core-shell structure enhances the bonding strength with the matrix. At the same time, the composite nucleating agent synergistically induces PA6 to form a mixed structure of α and γ crystals. The synergistic reinforcement mechanism of "interfacial γ crystal barrier - matrix α crystal toughening" effectively improves the tensile properties of the material. The reinforcement effect becomes more significant with increasing CNF content. The water vapor transmission rate of Example 1 to Example 3 gradually increased from 0.11 g / m 2 Gradually increased to 0.52 g / m2 over 24 hours 2.24h, further proving that there is a certain pore structure or active space between molecular chains inside the material, and the graphene oxide (GO) shell wrapped on the surface of the modified carbon nanofibers will interact with this change inside the material. When hydrogen molecules try to penetrate, these pore structures are divided into more tortuous paths by the GO shell. As a result, when hydrogen molecules encounter the "maze" structure constructed by the GO shell, the diffusion path is further extended, thereby improving the barrier effect on hydrogen molecules; From Example 1 to Example 2, the oxygen permeability increases significantly. This is because the increase in CNF content changes the material structure and reduces the oxygen barrier ability. However, from Example 2 to Example 3, the oxygen permeability is basically stable, indicating that when the CNF content reaches a certain level, its effect on the oxygen barrier performance no longer changes significantly.

[0041] In Comparative Example 1, the surface of the unmodified carbon nanofibers lacks polar groups, has poor compatibility with the matrix, and is easy to agglomerate, which makes it impossible to effectively disperse in the matrix and difficult to form a uniform reinforcement network. When the material is impacted, the stress cannot be effectively transmitted and dispersed, so the impact strength is only far lower than that of the embodiment. In addition, the agglomeration of the unmodified carbon nanofibers forms more defects and microcracks, which provide channels for the penetration of water vapor and oxygen, resulting in water vapor permeability and oxygen permeability higher than all embodiments, and the tensile strength is weakened due to the agglomeration phenomenon.

[0042] In Comparative Example 2, no composite nucleating agent was added. However, the composite nucleating agent can induce PA6 to form a mixed structure of α crystals and γ crystals. This mixed structure is crucial to improving the toughness of the material. In the absence of the composite nucleating agent, the PA6 crystal structure is imperfect and cannot effectively absorb impact energy, and the impact strength drops to the lowest among all categories.

[0043] In Comparative Example 3, anhydride-modified ethylene copolymer is not used, and the interfacial bonding between the carbon nanofibers and the matrix is ​​weak, which easily leads to interfacial debonding during the impact process, resulting in stress concentration. The impact strength and tensile strength are lower than those in the examples, while the water vapor permeability and oxygen permeability are higher than those in some examples.

[0044] In Comparative Example 4, plasma treatment was not performed, but the fluorocarbon barrier layer formed by plasma treatment can effectively block oxygen and water vapor, and thus, its water vapor permeability and oxygen permeability are respectively higher than those of some embodiments.

[0045] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container, characterized in that: The components, calculated by weight, include 0.5-1.2 parts of modified carbon nanofiber, 10-15 parts of anhydride-modified ethylene copolymer, and 84-89 parts of polyamide 6; The modified carbon nanofiber is a core-shell structure, wherein the core-shell structure has carbon nanofiber as a core and graphene oxide as a shell; the carbon nanofiber is grafted with amino groups; and the amino groups are electrostatically entangled with the graphene oxide.

2. The hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 1, characterized in that: It also includes 0.5 to 2 parts of a composite nucleating agent.

3. The hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 1, characterized in that: The composite nucleating agent includes nano-hydroxyapatite and organic phosphate; the weight ratio of the nano-hydroxyapatite to the organic phosphate is 1:1-1.

5.

4. A method for preparing a high-strength and high-toughness hydrogen storage container hydrogen barrier lining material according to any one of claims 1 to 3, characterized in that: The steps include: S1. Dispersing carbon nanofibers in deionized water, adding polyethyleneimine and stirring to react, washing by centrifugation until neutral, and freeze-drying to obtain amino-modified carbon nanofibers; S2. blending the amino-modified carbon nanofibers and the graphene oxide dispersion according to a certain proportion, centrifuging and freeze-drying to obtain modified carbon nanofibers; S3: banburying and blending the modified carbon nanofibers and the anhydride-modified ethylene copolymer to obtain a premix; S4 melt-blending the premix, polyamide 6 and composite nucleating agent, and extruding and granulating to obtain a molding masterbatch; S5: After annealing the molding masterbatch, plasma treatment is performed using a fluorocarbon precursor to obtain a finished material.

5. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S1, the parameters of the stirring reaction include: stirring temperature of 60-65° C., and stirring time of 4-6 h.

6. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S2, the ratio of the graphene oxide dispersion to the amino-modified carbon nanofibers is 1-1.2 mL: 2-2.5 g.

7. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S3, the parameters of the banburying blending include: a banburying temperature of 180-185° C., a banburying speed of 60-70 rpm, and a banburying time of 15-30 min.

8. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S4, the melt blending parameters include: an extrusion speed of 100-110 rpm, and the temperature of each zone is: 175-180° C. in zone 1, 190-195° C. in zone 2, 205-210° C. in zone 3, 220-225° C. in zone 4, 235-240° C. in zone 5, and 230-235° C. in zone 6.

9. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S4, the extrusion granulation parameters include: the heating temperature of each zone is: 210-212°C for zone 1, 215-218°C for zone 2, 223-225°C for zone 3, 220-223°C for zone 4, and 200-205°C for zone 5; the injection time is 10 s, the cooling time is maintained at 40 s, and the ejection time is 2 s.

10. The method for preparing a hydrogen barrier lining material for a high-strength and high-toughness hydrogen storage container according to claim 4, characterized in that: In step S5, the parameters of the plasma treatment include: treatment power of 100-300 W, treatment time of 5-30 min, and treatment temperature of 25-80°C.

Images